In ubiquitous computing applications, computing technology is integrated into the environment such that users may not even be aware of its operation in the background. In order for a ubiquitous computing application to be able to automatically perform operations on behalf of people (e.g. to control lighting or multimedia systems, to display messages in a location close to a user etc), the underlying computing system needs to be able to sense information about the state of the environment in which it operates. In particular, the system may want to know where people are in the environment, who those people are and what those people are doing in order to be able to determine what automated actions would be beneficial.
Existing systems for locating people typically monitor people entering and exiting rooms and require people to carry an electronic location device of some kind, such as an RFID (radio-frequency identification) tag. Alternatively, pressure sensing mats may be used at the entrances to rooms, however, such devices only indicate occupancy of a room and do not identify the particular occupant(s).
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known location systems.